Funds are requested for the purchase of a Mark I Cesium 137 gamma irradiator designed for whole body irradiation of mice, a capability that is lacking at the University of Georgia. Major research applications that require this instrument include 1) ablation of host bone marrow prior to transplantation for generating bone marrow chimeric mice, 2) irradiation of antigen presenting cells for use in studies of T cell activation and development, and 3) providing an environment for efficient growth and isolation of Trypanosoma cruzi parasites. The major users group comprises 10 NIH-funded researchers from four Departments at UGA. The only irradiator currently available to UGA investigators is a Gamma Cell 200 irradiator provided through the Center for Applied Isotope Studies and, due to its age and increasing unreliability, is in need of a replacement unit that can meet the needs of the growing number of immunologists at UGA. In addition, that instrument is not appropriate for irradiating live animals for immunological research. Acquisition of the proposed irradiator will provide new capabilities that will allow investigators to address complex immunological and cell biological research problems. Specific lines of investigation that will directly benefit from the purchase of the instrument include: T and B cell development and functions in infectious and autoimmune disease settings, antigen presentation and vaccine development, and the cell biology of T. cruzi, the causative agent of Chagas'Disease. The instrumentation will therefore facilitate the realization of research goals and maintenance of NIH support for biomedical research.